(1) Field of the Invention
This invention relates to a substrate heat treatment apparatus for heat-treating substrates such as semiconductor wafers and glass substrates for liquid crystal displays (hereinafter simply called substrates).
(2) Description of the Related Art
A conventional substrate heat treatment apparatus of the type noted above has a bake plate for supporting a substrate, and a cover for securing a heat-treating atmosphere above the bake plate. The cover has a heater. By controlling the temperature of the cover, a target temperature is attained in a short time even when a preset temperature is changed (as disclosed in Japanese Unexamined Patent Publications Nos. 1997-8049 and 1998-189429, for example).
A different apparatus has a construction for adjusting varied locations on a surface of a substrate placed on a bake plate relative to a cover, to adjust a temperature distribution over the surface of the substrate (as disclosed in Japanese Unexamined Patent Publication No. 2000-3843, for example).
These conventional apparatus have the following drawbacks.
With an increasingly refined pattern rule in the semiconductor manufacturing process in recent years, it has been desired to expedite throughput by raising a rate of temperature increase to a target temperature for heat treatment after feeding a substrate into an apparatus. Not only this, but it is also required to minimize the time taken in a temperature increasing process leading to the target temperature when a temperature distribution tends to be unstable, and to improve a transitional temperature distribution over the surface of the substrate. For this purpose, it is necessary to control the temperature of the cover, and to set the cover close to the bake plate. However, the cover and bake plate are subjected to separate temperature controls, and mutual heat interference would render the temperature controls difficult. The strong heating action of the bake plate can cause the temperature in the cover to overshoot the target temperature.